The present invention relates to a method and apparatus for maintaining an alignment between a reflector antenna and a source of electromagnetic radiation, and more particularly relates to a tracking system of a type having a reflector for reflecting electromagnetic radiation generated from a electromagnetic radiation source, a receiver, and a rotary sub-reflector positioned between the reflector and the radiation source for directing the radiation reflected by the reflector to the receiver and for generating triggering signals to provide a reading of the reflected radiation.
U.S. Pat. No. 5,457,464, issued on Oct. 10, 1995, discloses such a tracking system for monitoring alignment between a reflector antenna and a source of electromagnetic radiation. Arranged between the radiation source and the reflector of the reflector antenna is a rotatable sub-reflector which extends transversely to the longitudinal axis of the reflector for directing radiation reflected by the reflector onto a receiving element. The sub-reflector is formed as interrupter or attenuator, and includes one or more eccentric, radially opposing apertures for interrupting or attenuating regions of the radiation reflected by the reflector. The interrupter is formed by a pair of reflective disks, with each of the disks having formed therein the apertures. At a misalignment of the reflector, portions of the radiation are interrupted or attenuated by coinciding apertures and thus have different radiation strength or measuring signals. The chosen measuring signals are stored and compared in a comparator to generate a corrective signal for operating motors by which the reflector is then re-aligned.
This conventional tracking system has the drawback that the sub-reflector or interrupter is relatively complex and that the tracking system can only attenuate received signals. Moreover, this conventional tracking system requires the use of a so-called orthomode transducer which has an offset of about 90 degrees or two receiving elements which are arranged at a right angle to one another to correct a rotary phase misalignment.